How vapour rises up
Previous research has shown that water vapour enters the stratosphere through different sources; for instance, it can travel up through the tropopause, or the boundary between the troposphere and stratosphere. This movement is strongest in the tropics, Martin Jucker, climate scientist with University of New South Wales, Australia, tells Down To Earth (DTE). “The tropics are the one place on Earth where air generally moves upward in both the troposphere and the stratosphere. Due to this upward motion, which cools the air, the tropical tropopause is also where the troposphere is coldest,” he says.
Jucker adds that cold temperatures regulate how much water vapour enters the stratosphere. As air passes through the coldest part of the atmosphere, most water vapour is removed—a process known as “freeze drying”. Due to this, only trace amounts of water vapour remain as gas and enter the stratosphere. This is also the reason that stratospheric water vapour is at its minimum rate during…